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Hellow!
I want to edit and delete data in file(C/C++).

What I have tried:

I have tried this method
C++
 ifstream read, read1;
ofstream write, write1;

read.open("File.txt", ios::in);
write.open("Temp.txt");

int old, New, a;
cout << "Enter number you want to edit = ";
cin >> old;

cout << "Enter new number to replace ";
cin >> New;

while (!read.eof()) {
    read >> a;

    if (a == old) { write << New << endl; }
    else          { write << a << endl;   }
}

read.close();
write.close();

read1.open("Temp.txt", ios::app);
write1.open("File.txt");

while (!read1.eof()) {
    read1 >> a;
    write1 << a << endl;
}


And this code work well.
But the issue is that this process is very slow. I mean if there are thousand of lines in file and i want to edit or delete just one line then the process is very slow.
So i need some algorithm by using that i can able to edit or delete just that line i want.
So is there any algorithm or Function?

Thanks!
Posted
Updated 30-May-18 0:33am

You can avoid the second while loop which is just copying the content. Instead delete File.txt and then rename Temp.txt:
C++
// Deleting the file is only necessary if the used C library 
//  implementation does not support renaming to an existing file
remove("File.txt");
rename("Temp.txt", "File.txt");
That will make your application run about half the time of your code with large files.
 
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v2
I would do the following:

1) read the full file in a string
2) make than a string replace
3) and write the file

use std::string for supporting my plan ;-)
 
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Comments
Usama Iftikhar Butt 30-May-18 11:32am    
can you explain your idea little bit more

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